CBSE Class 12 Physics Wave Optics Worksheet

Question. Newton postulated his corpuscular theory of light on the basis of
(a) Newton’s rings
(b) rectilinear propagation of light
(c) colour through thin films
(d) dispersion of white light into colours.

Answer: B

Question. In Huygen’s wave theory, the loucs of all points in the same state of vibration is called
(a) a half period zone
(b) a wavefront
(a) a ray
(d) vibrator

Answer: B

Question. Huygen’s concept of secondary wave
(a) allows us to find the focal length of a thick lens
(b) is a geometrical method to find a wavefront
(c) is used to determine the velocity of light
(d) is used to explain polarisation

Answer: B

Question. Light waves are
(a) electromagnetic waves in nature
(b) cosmic rays
(c) infra–red rays
(d) invisible in atmosphere

Answer: A

Question. The electromagnetic waves travel with a velocity
(a) equal to the velocity of sound
(b) equal to the velocity of light
(c) less than the velocity of light
(d) greater than the velocity of light

Answer: B

Question. We shift Young’s double slit experiment from air to water.Assuming that water is still and clear, it can be predicted that the fringe pattern will
(a) remain unchanged
(b) disappear
(c) shrink
(d) be enlarged

Answer: C

Question. In Young’s double slit interference experiment, the distance between two sources is 0.1 mm. The distance of the screen from the sources is 20 cm. Wavelength of light used is 5460 Å. Then the angular position of the first dark fringe is
(a) 0.08°
(b) 0.16°
(c) 0.20°
(d) 0.32°

Answer: B

Question. In Young’s double slit interference experiment if the slit separation is made 3 folds the fringe width becomes
(a) 1/3 fold
(b) 3 fold
(c) 3/6 fold
(d) 6 fold

Answer: A

Question. Two slits separated by a distance of 1 mm are illuminated with red light of wavelength 6.5 × 10^–7 m. The interference fringes are observed on a screen placed 1 m from the slits.The distance between third dark fringe and the fifth bright fringe is equal to
(a) 0.65 mm
(b) 1.63 mm
(c) 3.25 mm
(d) 4.88 mm

Answer: B

Question. In Young’s double slit experiment if the slit widths are in the ratio 1 : 9, the ratio of the intensity at minima to that at maxima will be
(a) 1
(b) 1/9
(c) 1/4
(d) 1/3

Answer: C

Question. Two waves having the intensities in the ratio of 9 : 1 produce interference. The ratio of maximum to minimum intensity is equal to
(a) 10 : 8
(b) 9 : 1
(c) 4 : 1
(d) 2 : 1

Answer: C

Question. Two coherent monochromatic light beams of intensities I and 4 I are superposed. The maximumm and minimum possible intensities in the resulting beam are
(a) 5 I and I
(b) 5 I and 3 I
(c) 9 I and I
(d) 9 I and 3 I

Answer: C

Question. In the two separate set-ups of the Young’s double slit experiment, fringes of equal width are observed when lights of wavelengths in the ratio 1 : 2 are used. If the ratio of the slit separation in the two cases is 2 : 1, the ratio of the distances between the plane of the slits and the screen, in the two set ups in
(a) 4 : 1
(b) 1 : 1
(c) 1 : 4
(d) 2 : 1

Answer: A

Question. If an inteference pattern has maximum and minimum intensities in the ratio of 36 : 1 then what will be the ratio of amplitudes
(a) 5 : 7
(b) 7 : 4
(c) 4 : 7
(d) 7 : 5

Answer: A

Question. When viewed in white light, soap bubbles show colours because of
(a) interference
(b) scattering
(c) diffraction
(d) disperscion

Answer: A

Question. A diffraction pattern is obtained using a beam of red light.What happens if the red light is replaced by blue light
(a) no change
(b) diffraction bands become narrower and crowded together
(c) bands become broader and farther apart
(d) bands disappear

Answer: B

Question. Diffraction and interference indicate
(a) wave nature
(b) particle nature
(c) both (a) and (b)
(d) none of the above

Answer: A

Question. The condition for observing Fraunhofer diffraction from a single slit is that the light wavefront incident on the slit should be
(a) spherical
(b) cylinderical
(c) plane
(d) elliptical

Answer: C

Question. Sound waves do not exhibit
(a) refraction
(b) interference
(c) diffraction
(d) polarisation

Answer: D

Question. Polarisation of light proves the
(a) corpuscular nature of light
(b) quantum nature of light
(c) transverse nature of light
(d) longitudinal wave nature of light

Answer: C

Question. Light waves can be polarised because they
(a) have high frequencies
(b) have short wavelength
(c) are transverse
(d) can be reflected

Answer: C

Question. A single slit of width b is illuminated by a coherent monochromatic light of wavelength λ. If the second and fourth minima in the diffraction pattern at a distance 1 m from the slit are at 3 cm and 6cm respectively from the central maximum,what is the width of the central maximum ? (i.e. distance between first minimum on either side of the central maximum)
(a) 1.5 cm
(b) 3.0 cm
(c) 4.5 cm
(d) 6.0 cm

Answer: B

Question. A single slit of width 0.1 mm is illuminated by a parallel beam of light of wavelength 6000 Å and diffraction bands are observed on a screen 0.5 m from the slit. The distance of the third dark band from the central bright band is :
(a) 3 mm
(b) 9 mm
(c) 4.5 mm
(d) 1.5 mm

Answer: B

Question. The angular width of the central maximum in a single slit diffraction pattern is 60°. The width of the slitis 1μm.The slit is illuminated by monochromatic plane waves. If another slit of same width is made near it, Young’s fringes can be observed on a screen placed at a distance 50 cm from the slits. If theobserved fringe width is 1 cm, what is slit separation distance? 
(a) 75 μ m
(b) 100 μ m
(c) 25 μ m
(d) 50 μ m

Answer: C

Question. A mixture of light, consisting of wavelenght 590 nm and an unknown wavlength, illuminates Young’s double lit and gives rise to two overlapping interference patterns on the screen. The central maximum of both lights coincide.Further, it is observed that the third bright fringe of known light coincides with the 4^th bright fringe of the unknown light. From this data, the wavelength of the unknown light is
(a) 393.4 nm
(b) 885.0 nm
(c) 442.5 nm
(d) 776.8 nm

Answer: C

Question. A Young’s double slit experiment uses a monochromatic source. The shape of the interference fringes formed on a screen 
(a) straight line
(b) parabola
(c) hyperbola
(d) circle

Answer: C

Question. The condition for obtaining secondary maxima in the diffraction pattern due to single slit is
(a) a sin θ = nλ
(b) a sin θ = (2n - 1)λ/2
(c) a sin θ = (2n -1)λ
(d) a sin θ = nλ/2

Answer: B

Question. Consider a light beam incident from air to a glass slab at Brewster’s angle as shown in figure.
A polaroid is placed in the path of the emergent ray at point P and rotated about an axis passing through the centre and perpendicular to the plane of the polaroid. 

(a) For a particular orientation, there shall be darkness as observed through the polaroid
(b) The intensity of light as seen through the polaroid shall be independent of the rotation
(c) The intensity of light as seen through the polaroid shall go through a minimum but not zero for two orientations of the polaroid
(d) The intensity of light as seen through the polaroid shall go through a minimum for four orientations of the polaroid

Answer: C

Question. Two Polaroids P₁ and P₂ are placed with their axis perpendicular to each other. Unpolarised light I₀ is incident on P₁. A third polaroid P₃ is kept in between P₁ and P₂ such that its axis makes an angle 45° with that of P₁ . The intensity of transmitted light through P₂ is
(a) I₀/4
(b) I₀/8
(c) I₀/16
(d) I₀/2

Answer: B

Question. In Young’s double slit experiment, the slits are 2 mm apart and are illuminated by photons of two wavelengths λ₁ = 12000Å and λ₂ = 10000Å. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other ?
(a) 6 mm
(b) 4 mm
(c) 3 mm
(d) 8 mm

Answer: A

Question. The intensity at the maximum in a Young's double slit experiment is I0. Distance between two slits is d = 5l, where l is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at a distance D = 10 d ?
(a) I₀
(b) I₀/4
(c) 3/4 I₀
(d) I₀/2

Answer: D

Question. Unpolarised light of intensity 32 W m^–2 passes through three polarizers such that the transmission axis of the last polarizer is crossed with that of the first. The intensity of final emerging light is 3 W m^–2. The intensity of light transmitted by first polarizer will be
(a) 32 W m^–2
(b) 16 W m^–2
(c) 8 W m^–2
(d) 4 W m–2

Answer: B

Question. Figure shows a standard two slit arrangement witn slits S₁, S₂, P₁, P₂ are the two minima points on either side of P (figure). 

At P₂ on the screen, there is a hole and behind P₂ is a second 2-slit arrangement with slits S₃, S₄ and a second screen behind them.
(a) There would be no interference pattern on the second screen but it would be lighted
(b) The second screen would be totally dark
(c) There would be a single bright point on the second screen
(d) There would be a regular two slit pattern on the second screen

Answer: D

Question. A radar sends radiowaves of frequency v towards an aeroplane moving with velocity va. A change Dn is observed in the frequency of reflected waves which is higher than original frequency. The velocity of aeroplane is (v_a << c)
(a) c Δn/v
(b) 2cΔn/Δn
(c) cΔn/2v
(d) Δn/2cv

Answer: C

Question. A beam of light of λ = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between first dark fringes on either side of the central bright fringe is: 
(a) 1.2 cm
(b) 1.2 mm
(c) 2.4 cm
(d) 2.4 mm

Answer: D

Question. Aperture of the human eye is 2 mm. Assuming the mean wavelength of light to be 5000 Å, the angular resolution limit of the eye is nearly
(a) 2 minute
(b) 1 minute
(c) 0.5 minute
(d) 1.5 minute

Answer: B

Question. For a parallel beam of monochromatic light of wavelength 'λ', diffraction is produced by a single slit whose width 'a' is of the wavelength of the light. If 'D' is the distance of the screen from the slit, the width of the central maxima will be:
(a) Dλ/a
(b) Da/λ
(c) 2Da/λ
(d) 2Dλ/a

Answer: D

Question. A parallel beam of monochromatic unpolarised light is incident on a transparent dielectric plate of refractive index 1/√3 . The reflected beam is completely polarised. Then the angle of incidence is
(a) 30º
(b) 60º
(c) 45º
(d) 75º

Answer: A

Question. Consider sunlight incident on a slit of width 10⁴ Å. The image seen through the slit shall
(a) be a fine sharp slit white in colour at the centre
(b) a bright slit white at the centre diffusing to zero intensities at the edges
(c) a bright slit white at the centre diffusing to regions of different colours
(d) only be a diffused slit white in colour

Answer: A

Question. In a diffraction pattern due to a single slit of width 'a', the first minimum is observed at an angle 30° when light of wavelength 5000 Å is incident on the slit. The first secondary maximum is observed at an angle of : 
(a) sin^-1(1/4)
(b) sin^-1(2/3)
(c) sin^-1(1/2)
(d) sin^-1(3/4)

Answer: D

Question. If the polarizing angle of a piece of glass for green light is 54.74°, then the angle of minimum deviation for an equilateral prism made of same glass is
[Given, tan 54.74° = 1.414]
(a) 45°
(b) 54.74°
(c) 60°
(d) 30°

Answer: D

Question. In the Young’s double-slit experiment, the intensity of light at a point on the screen where the path difference is λ is K, (λ being the wave length of light used). The intensity at a point where the path difference is λ/4, will be: 
(a) K
(b) K/4
(c) K/2
(d) Zero

Answer: C

DIRECTIONS for : Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer from the following-
(a) Statement -1 is false, Statement-2 is true
(b) Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(c) Statement -1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1
(d) Statement -1 is true, Statement-2 is false

Question. Statement 1 : In Young’s double slit experiment if wavelength of incident monochromatic light is just doubled, number of bright fringe on the screen will increase.
Statement 2: Maximum number of bright lunge on the screen is inversely proportional to the wavelength of light used.

Answer: A

Question. Statement 1 : In YDSE number of bright fringe or dark fringe can not be unlimited
Statement 2 : In YDSE path difference between the superposing waves can not be more than the distance between the slits.

Answer: B

Question. Statement 1 : In YDSE, if a thin film is introduced in front of the upper slit, then the fringe pattern shifts in the downward direction.
Statement 2 : In YDSE if the slit widths are unequal, the minima will be completely dark.

Answer: A

Question. Statement 1 : In YDSE, if I₁ = 9I₀ and I₂ = 4I₀ then I_max/I_min = 25 .
Statement 2 : In YDSE I_max = (√I₁ + √I₂)² and I_min = (√I₁ - √I₂)2 

Answer: B

 

 

 

1 Which phenomenon of light shows the transverse nature of light ?. 

 

2 Define polarisation of light. 

 

3 What is the effect on the interference fringes if the monochromatic source is replaced by a source of white light?

 

4 What is the effect on the interference fringes if the monochromatic source of red is replaced by a source of blue light?

 

5 Which phenomenon of light could not be explained by wave theory? 

 

6 What is the angle between refracted and reflected light when the reflected light is completely polarised ?

 

7 Which is more observable diffraction of light or sound ? Justify . 

 

8 Explain the polarization of sun light by scattering in the atmosphere. 

 

9 State and prove Brewster’s law of polarisation. 

 

10 State Huygen’s postulates of wave theory 

 

11 What is the shape of the wave front produced by a ) a point source at finite distance b) a point source at infinite distance c) linear source.

 

12 Draw ray diagrams to show secondary wave fronts when a plane wave front incident on a) concave mirror b) convex mirror c) convex lens d) concave lens e) prism

 

13 Define wavefront .

Using Huygen’s construction draw a figure showing thepropagation of a plane wave refracting at a plane surface separating two media. Hence verify Snell’s law of refraction

 

14 How does the fringe width of interference fringes change, when the whole apparatus of Young’s experiment is kept in a liquid of refractive index 1.3 ?

 

15 State the differences between interference and diffraction. 

 

16 Define angular width and linear width of central maximum of diffraction at a single slit.

 

18 State Malus law of polarization and explain how will you represent Malus Law graphically?

 

19 Show that the resultant intensity of two light waves of same amplitude and frequency undergo interference is

I=4 I ₀ cos ²(Φ/2)

 

20 What is the effect on the interference fringes in a Young’s double-slit experiment due to each of the following operations:

 

(a) the screen is moved away from the plane of the slits;

(b) the (monochromatic) source is replaced by another (monochromatic) source of shorter wavelength;

(c) the separation between the two slits is increased;

(d) the source slit is moved closer to the double-slit plane;

(e) the width of the source slit is increased;

(f ) the monochromatic source is replaced by a source of white light?

 

 

 1 Two slits are made one millimetre apart and the screen is placed one metre away. What is the fringe separation when bluegreen light of wavelength 500 nm is used?

 

2 For what distance is ray optics a good approximation when the aperture is 3 mm wide and the wavelength is 500 nm?

 

3 Assume that light of wavelength 6000Å is coming from a star. What is the limit of resolution of a telescope whose objective has a diameter of 100 inch?

 

4 Two slits are made one millimetre apart and the screen nis placed one metre away. What is the fringe separation when blue green light of wavelength 500 nm is used?

 

5 The angle of polarisation is 53° for a medium calculate the refractive index and critical angle of the medium.

 

6 In Young’s double-slit experiment using monochromatic light of wavelength λ, the intensity of light at a point on the screen where path difference is λ, is K units. What is the intensity of light at a point where path difference is λ/3?

 

7 Two polaroids are set in crossed positions. A third polaroid is placed between the two making an angle θ with the pass axis of the first polaroid. Write the expression of the intensity of light transmitted from the second polaroid. In what orientations will the transmitted intensity be

(i) minimum and (ii) maximum?

 

8 In Young’s double slit experiment, monochromatic light of wavelength 630 nm illuminates the pair of slits and produces an interference pattern in which two consecutive bright fringes are separated by 8 . 1 mm. Another source of monochromatic light produces the interference pattern in which the two consecutive bright fringes are separated by 7.2 mm. Find the wavelength of light from the second source